Manufacturing method for reflection type liquid crystal display

ABSTRACT

On an insulating substrate, there are formed a first gate electrode, a gate insulating film, a semiconductor film, and an interlayer insulating film. Above the interlayer insulating film, a TFT is formed having a second gate electrode connected to the first gate electrode. Then, a photosensitive resin is formed over the entire surface of the extant layers. Subsequently, first exposure is applied using a first mask, and second exposure is then applied using a second mask with a larger amount of light than used for the first exposure. The second mask has an opening at a position corresponding to a source. Thereafter, the photosensitive resin film is developed thereby forming a contact hole and a concave.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation in part application of U.S.patent applications Ser. No. 09/615,608, filed on Jul. 14, 2000, andSer. No. 09/447,378, filed on Nov. 23, 1999, both of which areincorporated herein in their entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention:

[0003] The present invention relates to a liquid crystal display device.

[0004] 2. Description of the Related Art:

[0005] Various conventional liquid crystal displays (LCDs) have beenknown. A particular example is an LCD of active matrix type, whichcomprises a thin film transistor (TFT) for controlling connectionbetween a data line and a pixel electrode (a display electrode) forevery pixel to thereby control display for each pixel.

[0006] A vertical alignment type of LCD, in which control of liquidcrystal alignment is important, is also known. Japanese PatentApplication Laid-open No. Hei 7-311383, for example, discloses formationof concaves and convexes on the surface of each pixel where it contactsliquid crystal, to therewith control the alignment of the liquidcrystal.

SUMMARY OF THE INVENTION

[0007] The present invention aims to enable efficient manufacturing of aliquid crystal device having an electrical conductive film with aconcave formed thereon.

[0008] According to the present invention, a photosensitive resin isexposed twice using two different masks before developing such thatconvexes of two different depths are formed on the resin. This enablesreduction of the number of steps required to form convexes of twodifferent depths.

[0009] In particular, a convex (a through hole) having one depth is usedto constitute a contact hole, that communicates a thin film transistorand an electrical conductive film (a display electrode) of a sizecorresponding to a pixel, and a convex having another depth is used as aconvex formed on the picture electrode. Moreover, the sloping surface ofthe convex is utilized to control the alignment of liquid crystals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other objects, features, and advantages of thepresent invention will become further apparent from the followingdescription of an exemplary embodiment taken in conjunction with theaccompanying drawings wherein:

[0011] FIGS. 1(a), 1(b), 1(c), 1(d), 1(e) are cross sectional diagramsshowing manufacturing steps in an exemplary embodiment;

[0012]FIG. 2 is a plan view showing a liquid crystal device;

[0013]FIG. 3 is a cross sectional diagram showing a liquid crystaldevice;

[0014] FIGS. 4(a) , 4(b), 4(c), 4(d), 4(e) are cross sectional diagramsshowing manufacturing steps in another exemplary embodiment;

[0015]FIG. 5 is a cross sectional diagram showing a liquid crystaldevice of still another exemplary embodiment;

[0016]FIG. 6 is a diagram showing an exemplary structure of a convexportion; and

[0017]FIG. 7 is a cross sectional diagram showing a liquid crystaldevice in still another exemplary embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following, a manufacturing method for a reflection typeLCD according to the present invention will be described.

[0019] FIGS. 1(a) to 1(e) are cross sectional views, along the line A-Ain FIG. 2, showing manufacturing steps for a LCD of the presentinvention.

[0020] As shown in FIG. 2, a TFT is formed in an area close to eachintersection of a gate signal line 51 and a drain signal line 52. Thegate signal line 51 includes a first gate electrode 11, while the drainsignal line 52 includes a drain electrode 16. A display electrode 28,which comprises electrically conductive material, is connected to theTFT. The display electrode 28 is provided extending above the TFT, andhas a surface with concaves 27 formed thereon.

[0021] Step 1 (FIG. 1(a)) on an insulating substrate 10, there aresequentially formed a first gate electrode 11, a gate insulating film12, and an active layer 13, wherein the insulating substrate 10comprises a quartz glass, a non-alkali glass, and so on, the first gateelectrode 11 constitutes a part of the gate signal line 51 and comprisesrefractory metal (Cr, Mo, and so on), the gate insulating film 12comprises a SiN film and a SiO₂ film, and the active layer 13 comprisesa polycrystalline silicon film.

[0022] In the active layer 13, there are formed a channel 13 c above thefirst gate electrode 11, and a source 13 s and a drain 13 d at therespective sides of the channel 13 c. The source 13 s and the drain 13 dare formed through ion implantation.

[0023] On the channel 13 c, there is formed a stopper insulating film14, comprising a SiO₂ film, as a mask covering the channel 13 c forpreventing ion intrusion at the time of ion implantation.

[0024] Covering the entire surface of the gate insulating film 12, theactive layer 13, and the stopper insulating film 14, there is formed aninterlayer insulating film 15, which comprises laminated SiO₂ film, SiNfilm and SiO₂ film. The interlayer insulating film 15 may be formed ofeither a single layer of organic material such as SiO, SiN, acrylic, andso on, or multiple layers of combinations of any thereof.

[0025] Then, contact holes l6, 17 are formed in the interlayerinsulating film 15 at respective positions corresponding to the drain 13d and the source 13 s. The contact hole 16, corresponding to the drain13 d, is filled by metal, specifically, by a single Al layer orsequentially laminated Mo and Al layers, thereby forming a drainelectrode 18. At the same time as formation of the drain electrode 18, asecond gate electrode 19 is formed on the interlayer insulating film 15above the channel 13 c. That is, a second gate electrode 19 is formedusing metal such as a single Al layer or laminated Mo and Al layers.

[0026] The second gate electrode 19 is connected to the gate signal line51 on the insulating substrate 10, via a contact hole 20, formed in thegate insulating film 12 and the interlayer insulating film 15.

[0027] A drain signal line 52 is formed on the interlayer insulatingfilm 15 at the same time as formation of the drain electrode 18, whichconstitutes a part of the drain signal line 52.

[0028] Step 2 (FIG. 1(b)): a photosensitive resin film 70, made ofinsulating resin having photosensitivity and an even surface, is formedover the entire surface of the interlayer insulating film 15, includingthe contact hole 17, the drain signal line 52, the drain electrode 18,and the second gate electrode 19. Thereafter, a first mask 71 having anopening at a position corresponding to a concave 27 to be formed on anarea where a display electrode 28 is to be formed, is placed beforefirst exposure 75 is applied. The amount of exposure is determined suchthat the light reaches a point at a shallow depth below the surface ofthe photosensitive resin 70, specifically, 20 mJ/cm² to 60 mJ/cm²,preferably 25 mJ/cm² to 50 mJ/cm², and more preferably 30 mJ/cm² to 40mJ/cm².

[0029] Note that specific examples of photosensitive resin may beacrylic resin or polyimide.

[0030] Step 3 (FIG. 1(c)): the first mask 71 is removed, and a secondmask 72 is placed instead. The second mask 72 has an opening at aposition corresponding to a place where a contact hole 73 for connectionbetween the source 13 s of the active layer 13 and the display electrode28 is to be formed.

[0031] After the deposition of the second mask 72, second exposure 76 isapplied. The amount of the second exposure is larger than that for thefirst exposure so that a deeper contact hole 73 than the concave 74 canbe formed. That is, in order for the exposure light to reach deeper,specifically, deep enough to form a contact hole 73 reaching the source13 s, the amount of second exposure 76 must be large enough,specifically, 200 mJ/cm² to 600 mJ/cm², preferably 250 mJ/cm² to 500mJ/cm², more preferably, 300 mJ/cm² to 400 mJ/cm².

[0032] Step 4 (FIG. 1(d)): after the second mask 72 is removed, thephotosensitive resin film 70 is developed whereby a concave 74 and acontact hole 73 are formed.

[0033] After the formation of the concave 74 and the contact hole 73 asdescribed above, a display electrode 28, made of a transparentsemiconductor material such as ITO, is formed thereon. With the above,the contact hole 17 (corresponding to 73 in FIG. 1) and the concave 27(corresponding to 74 in FIG. 1) are completed.

[0034] In addition, an alignment layer for aligning liquid crystal isformed on the display electrode 28. Formation of the alignment filmcompletes a TFT substrate. Then, opposing the TFT substrate, an opposingelectrode substrate is formed, which has an opposing electrode and analignment layer formed on the side thereof having liquid crystal, and aretardation film and a polarizer formed on the other side thereofwithout liquid crystal (i.e., on the observer side). The TFT substrateand the opposing electrode substrate are attached to each other alongthe edges thereof and liquid crystal is filled into the space betweenthem, so that a reflection type LCD is completed.

[0035] It should be noted that the opposing electrode substrate issubstantially transparent, and is not segmented for every pixel.

[0036] Further, as shown in FIG. 3, an alignment film 80 is formed overthe entire surface of the display electrode 28 for aligning the liquidcrystal. With the above, a TFT substrate 82 completes. Moreover, anopposing electrode substrate 90 is provided opposing to the TFTsubstrate 82 via the liquid crystal 84.

[0037] The opposing electrode substrate 90 comprises a transparentsubstrate 92, similar to the substrate 10, having opposing electrodes 94and an alignment film sequentially stacked on the surface thereof closerto the liquid crystal 84. Further, the TFT substrate 82 and the opposingelectrode substrate 90 are attached to each other at the peripheriesthereof, and liquid crystal 84 is enclosed in the space between the TFTsubstrate 82 and the opposing electrode substrate 90.

[0038] A polarization panel (not shown) is provided outside thesubstrate 10 and outside the substrate 92. For color display, aprotective film and R, G, B color filters, having a light shieldingblack matrix, are provided between the substrate 92 and the opposingelectrode 94 of the opposing electrode substrate 90.

[0039] As described above, the use of photosensitive resin and exposurewith the photosensitive resin using different amounts of light forformation of a desired contact hole and a concave, readily enableformation of a contact hole and a concave without the need of twoformations of a planarization insulating film, as is conventionallyneeded. Therefore, the manufacturing process can be simplified, andcosts can be reduced.

[0040] It should be noted that the present invention is not limited tothe above embodiment, in which a concave and a contact hole are formedby development. Moreover, heating at, e.g., about 220 after thedevelopment would make more gently slanting edges of the concave 74, asshown in FIG. 1(e).

[0041] Also, the present invention is not limited to the aboveembodiment, in which concaves 27 are formed as two analogous rectanglesformed in a reflection display electrode formation area, and the concave27 may rather be formed in a circle or in two or more different shapesinstead. Moreover, the number of the concave 27 is not limited to two,as described above, and a single concave 27 or three or more concaves 27may be formed instead.

[0042] Further, the area where the concave 27 is formed is not limitedto an area enclosed by the gate signal line 51 and the drain signal line52, and the concave 27 may rather be formed in an area overlapping thegate signal line 51 or the drain signal line 52.

[0043] Still further, the present invention is not limited to the aboveembodiment, in which the circumferential edges of adjacent displayelectrodes 28 overlap the gate signal line 51 and the drain signal line52, and the edge may rather overlap either one of the gate signal line51 and the drain signal line 52 or may even not overlap the signal line.Yet further, the display electrode 28 may not extend over the TFT.

[0044] Moreover, the insulating film between the second gate electrode17 and the active layer 13, i.e., the stopper insulating film 14, theinterlayer insulating film 15, and the planarization insulating film 19in this embodiment, may each be constituted of a single SiO, SiN, or anyorganic film, or a laminated combination thereof.

[0045] Also, instead of the above described TFT having a double gateelectrode structure, having two gates, a single gate structure, havingone gate, or a multiple gate structure, having two or more gates, may besimilarly applicable.

[0046] The order of formation of the contact hole 72 and the concave 74may be reversed from that shown in FIGS. 1(a) to 1(e), into that shownin FIGS. 4(a) to 4(e). With the reversed order, exposure for formationof the contact hole 73, as shown in FIG. 4(b), is initially applied,followed by exposure for formation of the concave 74, as shown in FIG.4(c). In this case, FIGS. 4(a), 4(d), 4(e) are identical to FIGS. 1(a),1(d), 1(e), FIG. 4(b) is identical to FIG. 1(c), and FIG. 4(c) isidentical to FIG. 1(b).

[0047] Here, the alignment films 80, 96 are made of an organic resin,such as polyimide, serving as a vertical alignment film for verticalalignment of crystal liquid 84 having negative dielectric anisotropic.The alignment films 80, 96 do not require rubbing. It should be notedthat liquid crystal having positive dielectric anisotropic may beemployed for the liquid crystal 84.

[0048] For the liquid crystal 84 comprising liquid crystal havingnegative dielectric anisotropic, liquid crystal molecules are alignedvertically with respect to the substrate when no voltage is applied, andaligned substantially parallel to the substrate when a voltage isapplied.

[0049] In an exemplary embodiment, in which a concave 74 is formed, theconcave 74 serves to control, via the sloping surface thereof, liquidcrystal alignment. Specifically, for the liquid crystal 84 comprisingliquid crystal having negative dielectric anisotropic, the liquidcrystal molecules are aligned vertical to the surface of the alignmentfilm 80 when no voltage is applied. Therefore, the liquid crystalmolecules located in the upper portion of the sloping surface of theconcave 74 now have an alignment direction inclined, so that the liquidcrystal molecules within a pixel are divided. This serves to widen theviewing angle.

[0050] Further, preferably, a concave 74 may be formed in a large size,leaving the rest as a convex. That is, as shown in FIG. 5, the concave74 may be formed extending over the substantially entire surface of thepixel with a part thereof forming a convex 100. This makes it possibleto control the alignment of the liquid crystal 84 by utilizing thesloping surface of the convex 100.

[0051] A method for controlling the alignment direction of liquidcrystal referred to as Multi-domain Vertical Alignment (MVA) isdisclosed in Japanese Patent Application Laid-open No. Hei 7-311383,which is incorporated herein in its entirety.

[0052] Preferably, the convex 100 has a shape as shown in FIG. 6.Specifically, two or more larger and smaller>shapes, two Y shapesconnected up-and-down symmetrically, an X shape, an elongated shape, anda diagonal line shape are all preferable.

[0053] With such a convex 100 formed, the sloping surface of the convex100 serves as an alignment control portion for controlling the alignmentof the liquid crystal 84. Note that a concave 74 may be formed in any ofthe shapes shown in FIG. 6.

[0054] Formation of an alignment control portion on a pixel as describedabove results in a portion incapable of displaying an image thereabove.In this view, preferably, a data line is provided on the alignmentcontrol portion, in particular, a convex.

[0055]FIG. 4 is a plan diagram showing a liquid crystal display devicein another exemplary embodiment.

[0056] As shown in FIG. 4, a plurality of gate signal lines 55 eachhaving integrally formed gate electrode 11 are disposed horizontally,and a plurality of drain signal lines 52 are disposed vertically. Athin-film transistor (TFT), which is a switching element, is disposed inthe vicinity of each intersection of the gate signal line 55 and thedrain signal line 52, and a pixel electrode 19 made of a transparentconducting material such as ITO is connected to the TFT.

[0057] In FIG. 4, the convex 100 has a shape in which the bottom end ofletter Y has the same forked shape as the top end, namely two letters Yare mutually connected with one of them turned upside down. In otherwords, the convex 100 has a shape that either end of its center region,which is rectangular and extending in a longitudinal direction of eachpixel, is forked into two to extend toward two corners of the pixel.

[0058] A feature of this embodiment is that the drain signal line 52 isformed along the convex portion 100 disposed on the substrate. In FIG.4, the drain signal line 52 in the vicinity of the TFT enters the pixelregion from its upper left, bends to extend in the lower right-handdirection to follow a branch section 100 at the upper left part of theconvex portion 100 a, and at a section 100 b of the convex portion 100extending vertically in FIG. 4, extends vertically in the same way. Thedrain signal line 52 further bends to extend in the lower left directionto follow a branch section 100 c extending in a lower left direction ofthe convex portion 100, leaves the pixel from its lower left, andextends to a pixel in the next row. Thus, the drain signal line 52 isdisposed to overlap with the left-side branch sections and the verticalsection of the convex portion 100.

[0059] The liquid crystal immediately above the convex portion 100 keepsa vertically aligned state because an electric field is not produced andthe alignment is not controlled. Therefore, it becomes a light-shieldingregion that always does not allow the passage of light. In thisembodiment, the drain signal line 52 which is a metal line and has alight-shielding function is disposed there, so that the twolight-shielding regions are overlapped. As a result, the light-shieldingregion occupying the pixel region becomes small, and an aperture ratiois improved. The region immediately below the convex portion 100 is aboundary of the liquid crystal in its alignment direction in the pixel,so that the alignment direction tends to be disturbed. When thealignment direction is disturbed, light may leak erroneously. But, sincethe drain signal line 52 having the light-shielding function is disposedin this embodiment, the present invention can prevent the light fromleaking and can further enhance contrast.

What is claimed is:
 1. A manufacturing method for a liquid crystaldisplay, said method comprising: forming a photosensitive resin film ona substrate; exposing the photosensitive resin film with a first amountof light via a first mask; exposing the photosensitive resin film with asecond amount of light via a second mask; developing the photosensitiveresin film subjected to two exposures thereby forming two types ofconcaves having different depths; and forming an electrical conductivefilm on the photosensitive resin film developed to have two types ofconcaves.
 2. A manufacturing method according to claim 1, furthercomprising forming a thin film transistor on the substrate so that thephotosensitive resin film is formed thereon, wherein the photosensitiveresin film constitutes an insulating film, the electrically conductivefilm is a pixel electrode having a size corresponding to a pixel, andthe pixel electrode is electrically connected to the thin filmtransistor.
 3. A manufacturing method according to claim 2, wherein thefirst amount of light is larger than the second amount of light, theconcave formed using the first mask is a hole piercing through thephotosensitive resin film, constituting a contact hole for electricallyconnecting the pixel electrode and the thin film transistor, and theconcave formed using the second mask constitutes a concave formed on asurface of the pixel electrode.
 4. A manufacturing method according toclaim 2, wherein the second amount of light is larger than the firstamount of light, the concave formed using the first mask constitutes aconcave formed on a surface of the pixel electrode, and the concaveformed using the second mask is a hole piercing through thephotosensitive resin film, constituting a contact hole for electricallyconnecting the pixel electrode and the thin film transistor.
 5. Amanufacturing method according to claim 1, further comprising heatingthe photo sensitive resin to give edges of the concave a gentler slope.6. A manufacturing method for a liquid crystal display, said methodcomprising: forming a photosensitive resin film on a substrate; exposingthe photosensitive resin film with a first amount of light via a firstmask; exposing the photosensitive resin film with a second amount oflight via a second mask; developing the photosensitive resin film bysubjecting it to two exposures, thereby forming a hole piercing thephotosensitive resin film and a concave not piercing the photosensitiveresin film; and forming an electrical conductive film on thephotosensitive resin film having two kinds of convexes and beingdeveloped, such that the hole piercing is used as a contact hole and asloping surface of the concave is used as an alignment control portion.7. A method according to claim 6, wherein the concave is formedsubstantially over the entire surface of the pixel, leaving the rest ofthe surface convex.